These teachings relate generally to the fabrication and use of antimicrobial nanoemulsions for the treatment of foods and surfaces.
Emulsions containing very fine droplets (radius≈<100 nm) are referred to as nanoemulsions. Nanoemulsions can be formed from both high-energy and low-energy methods. High energy methods require specialized mechanical devices that are capable of generating intense mechanical forces that can intermingle and disrupt the oil and water phases, such as sonicators, high pressure valve homogenizers, or microfluidizers. Low-energy methods rely on the spontaneous formation of fine oil droplets due to physicochemical processes that occur when certain combinations of surfactant, oil, and water are combined under appropriate conditions The use of low-energy methods is highly attractive for preparing nanoemulsions for many applications because of its low cost and simplicity. A number of low-energy methods are available for producing nanoemulsions, e.g., spontaneous emulsification, emulsion inversion point, phase inversion temperature, and phase inversion composition methods. The spontaneous emulsification method is one of the suitable for commercial implementation since it simply involves titrating a mixture of oil and water-soluble surfactant into water. This method has recently been reported to be suitable for application in the food industry for fabricating effective antimicrobial nanoemulsions from essential oils.
Essential oils are natural compounds that are isolated from various plant sources such as thyme, oregano, and basil that demonstrate antimicrobial activity. One essential oil that has been shown to have promising antimicrobial properties against a variety of foodborne pathogens is carvacrol. Essential oils, alone, have minimal solubility in water.
The use of essential oils, such as carvacrol, as antimicrobials is appealing because these compounds are a “natural” alternative to traditional treatment methods. The effectiveness of carvacrol against various foodborne pathogens has been reported in numerous studies. The antimicrobial efficacy of carvacrol has been attributed to its ability to permeabilize and depolarize the cytoplasmic membrane. This phenomenon is a result of the hydrophilic hydroxyl group on the phenolic ring, which allows carvacrol to dissolve into and disrupt cytoplasmic membrane function. However, even with this hydrophilic moiety, carvacrol is still predominantly hydrophobic and therefore has low water-solubility.
Both acetic and levulinic acid are proven antimicrobial compounds that have wide acceptability in the food safety community. Organic acids have a direct impact on the intracellular pH of pathogens. Protonated organic acids can pass through the outer membrane of bacteria and once in the cytoplasm, dissociate, releasing protons and anions inside the cell. This sudden influx of charged compounds disrupts a cells homeostasis by acidifying the cytoplasm. If acid levels are high enough, functional enzyme denaturation will occur ultimately leading to cell death.
In view of the number of the possible applications for the treatment of fruits and surfaces, there is a need for a method for preparing stable nanoemulsions with desired antimicrobial performance.